Linked List Node assigning
I have a binary B+tree.
I have done all the insertion..but I have a major problem as my current node is poiting to the last node I inserted node ...
In the class I have a parent node
I want to use this to go back to the root...but I fail..function is called from a tree class
in the function {
Node curr = this;
Node temp= this.parent;
while(temp!=null) {
temp= temp.parent;
if(temp!=null) {
curr=temp;
return curr;
However, this code doesn't work...
not sure why...
can anyone help me with this .. Thanks?
carl33p wrote:
Might have to fill it manually unless anyone else has an idea.
...I have a few ideas:
- keep the logic from getting input from a user separate from your linked list
class: it is not the responsibility of a linked list to perform such tasks;
- create a separate class with a main method that instantiates a linked list
and gets the user input;
- don't name one of your classes the same as one of Java's "core" classes. When
you do "import java.util.*" you might get in trouble. Since you are only storing
int's in your list, a better name would be "IntLinkedList"
- create a method called add(int) that is responsible for the addition of new
nodes;
- create a private inner class for your Node class: you won't be needing this
Node outside of your IntLinkedList class, so there's no need for it to be
"visible" for other classes.
Here's a skeleton:
class Test {
private static int getUserInput() {
// Prompt the user to enter an integer and when
// a valid integer is entered, return it.
return -1;
public static void main(String[] args) {
IntLinkedList myList = new IntLinkedList();
int nodeCount = 5;
while(nodeCount-- > 0) {
int input = getUserInput();
myList.add(input);
System.out.println("myList = "+myList.toString());
class IntLinkedList {
private Node start;
public IntLinkedList() {
start = null;
public void add(int value) {
Node newNode = new Node(value);
// Your code here
// - what to do when 'start' equals null?
// - and what to do when 'start' does not equal null?
// more methods
private class Node {
int value;
Node next;
Node(int v) {
value = v;
next = null;
// more methods
}
Similar Messages
-
Hi,
In a lecture a couple of weeks ago, we began the topic of reference-based lists. I copied the attached
code off the board. I'm now trying to utilize the code by creating a public class Node. However, the constructors don't seem to make much sense. I was too busy writing down the information to pay much attention at the time. My book doesn't seem to address this...
1) in the first constructor: item = null; I'm declaring item initially as an integer, but the constructor is trying to attach a null to item. I think the intent is to create a node that initially has both info and link as nulls.
2) in the third constructor: link = Node; Is this possible? I'm not what this will do.
And finally, the second and third constructors are using the same name and parameter, so there is a conflict. I don't know how to resolve this.
Thanks in advance for any help...
aiki
public class Node {
public int info;
public Node link;
public Node(){
info = null;
link = null;
public Node (int data){
info = data;
link = null;
public Node (int data){
info = data;
link = Node;public class Node {
public int info;
public Node link;
public Node(){
// default constructor does nothing.
// Therefore info and link will get default values.
// For Objects this will be null
public Node (int data){
info = data;
// don't initialise link. See above
public Node (int data, Node node){
// I think you missed the second parameter
info = data;
link = node;
} -
Hello people!
I have problems with sorting a doubly linked list, I have kind of got stuck just looking at the code and don't really know what I'm doing anymore...
public void sortList()
int flag = 0;
DoubleNode temp; //Doubly Linked List Node
temp = firstNode;
String tempData;
while (flag != 1)
flag = 1;
String data = (String)temp.element;
while (temp.next != null)
int comp = data.compareTo((String)temp.next.element);
if (comp > 0)
tempData = (String)temp.element;
temp.element = temp.next.element;
data = (String)temp.element;
temp.next.element = tempData;
flag = 0;
else
temp = temp.next;
data = (String)temp.element;
I'm trying to take an easy way around the problem by not swaping nodes but just the data the nodes contain. I'm pretty new to this and my prof. has just gone insane giving us this hardcore assignment.
is this code even close to be correct?
is this a good way of tackling the problem?
thanks a lot! / DanOkay, without going into any great detail about possible issues with the algorithm or code, it's gonna first be necessary to know some more about the DoubleNode class. For example, does it have a next method? If it does, then right off the bat your code will have to be adjusted so that where you have written "temp.next" you actually call the next method (which, if it is parameterless, would be "temp.next()"). As you have it written now, "temp.next" is accessing the "next" attribute of your DoubleNode instance, and I don't think that's what you're intending.
-dSn -
I am confused at how to make a linked list using recursion. I've been looking at the syntax and examples from the web for the past couple hours, but all seem to be based on an empty .java file. I need to put it in my code somehow. here's the code segment:
public static boolean RecursiveTest (String s, int start, Node n) {
// The linked list
Node<char> bracket = new Node<char>();
int size = s.length();
char v = s.charAt(start);
//String sElement = parens.top();
boolean isGood = true;
// ending "ifs"
if (size == 0) { System.out.println("empty string"); return false; }
if (start == size) return isGood;
if (s.charAt(start) == '(' || s.charAt(start) == '[' ||
s.charAt(start)== '{') {
v.Push(sChar);
System.out.println(sChar);
return RecursiveTest(start+1, s.charAt(start));
else if (sChar.equals(")") && sElement.equals("(")) {
parens.Pop();
System.out.println(sChar);
return RecursiveTest(start+1);
else if (sChar.equals("]") && sElement.equals("[")) {
parens.Pop();
System.out.println(sChar);
return RecursiveTest(start+1);
else if (sChar.equals("}") && sElement.equals("{")) {
parens.Pop();
System.out.println(sChar);
return RecursiveTest(start+1);
else if (sChar.equals(")") && !sElement.equals("(")) {
System.out.println("bad");
isGood = false;
return isGood;
else if (sChar.equals("]") && !sElement.equals("[")) {
System.out.println("bad");
isGood = false;
return isGood;
else if (sChar.equals("}") && !sElement.equals("{")) {
System.out.println("bad");
isGood = false;
return isGood;
else return RecursiveTest(start+1);
} // end of RecursiveTest
I'm passing a string, 0, and a new node (i dunno about the last one there), from an above main class.
This code is wrong, i know, but it's all I got done so far. How would I be able to make a linked list inside this method?No one knows how to do a linked list inside a recursive method?Yes we do, but you have to realize that a list (whether it be a linked list
or an array list or whatever) has nothing to do with recursion per se.
If that list has to keep track of some state it certainly mustn't be created
within that recursive method as a local variable. And (see my previous
reply), what do you need recursion for? Counting and pairing brackets
can easily be done using an iterative method where the list keeps track
of the last seen left bracket (of any type).
kind regards,
Jos -
Splitting a Linked List at a Given Node, into Two Sublists??
My code just will not work!! Any help would be appreciated! My problem is in the last method SplitAt. These are the conditions set and my code:
Splitting a Linked List at a Given Node, into Two Sublists
a. Add the following as an abstract method to the class
LinkedListClass:
public void splitAt (LinkedListClass<T> secondList, T item);
//This method splits the list at the node with the info item into two sublists.
//Precondition: The list must exist.
//Postcondition: first and last point to the first and last nodes of the first sublist,
// respectively. secondList.first and secondList.last point to the first
// and last nodes of the second sublist.
Consider the following statements:
UnorderedLinkedList<Integer> myList;
UnorderedLinkedList<Integer> otherList;
Suppose myList points to the list with the elements 34, 65, 18, 39, 27, 89, and 12 (in this order). The statement
myList.splitAt(otherList, 18);
splits myList into two sublists: myList points to the list with elements 34 and 65, and otherList points to the sublist with elements 18, 39, 27, 89, and 12.
b. Provide the definition of the method splitAt in the class UnorderedLinkedList. Also write a program to test your method.
public class UnorderedLinkedList<T> extends LinkedListClass<T>
//Default constructor
public UnorderedLinkedList()
super();
//Method to determine whether searchItem is in
//the list.
//Postcondition: Returns true if searchItem is found
// in the list; false otherwise.
public boolean search(T searchItem)
LinkedListNode<T> current; //variable to traverse
//the list
boolean found;
current = first; //set current to point to the first
//node in the list
found = false; //set found to false
while (current != null && !found) //search the list
if (current.info.equals(searchItem)) //item is found
found = true;
else
current = current.link; //make current point to
//the next node
return found;
//Method to insert newItem in the list.
//Postcondition: first points to the new list
// and newItem is inserted at the
// beginning of the list. Also,
// last points to the last node and
// count is incremented by 1.
public void insertFirst(T newItem)
LinkedListNode<T> newNode; //variable to create the
//new node
newNode =
new LinkedListNode<T>(newItem, first); //create and
//insert newNode before
//first
first = newNode; //make first point to the
//actual first node
if (last == null) //if the list was empty, newNode is
//also the last node in the list
last = newNode;
count++; //increment count
//Method to insert newItem at the end of the list.
//Postcondition: first points to the new list and
// newItem is inserted at the end
// of the list. Also, last points to
// the last node and
// count is incremented by 1.
public void insertLast(T newItem)
LinkedListNode newNode; //variable to create the
//new node
newNode =
new LinkedListNode(newItem, null); //create newNode
if (first == null) //if the list is empty, newNode is
//both the first and last node
first = newNode;
last = newNode;
else //if the list is not empty, insert
//newNode after last
last.link = newNode; //insert newNode after last
last = newNode; //set last to point to the
//actual last node
count++;
}//end insertLast
//Method to delete deleteItem from the list.
//Postcondition: If found, the node containing
// deleteItem is deleted from the
// list. Also, first points to the first
// node, last points to the last
// node of the updated list, and count
// is decremented by 1.
public void deleteNode(T deleteItem)
LinkedListNode<T> current; //variable to traverse
//the list
LinkedListNode<T> trailCurrent; //variable just
//before current
boolean found;
if ( first == null) //Case 1; the list is empty
System.err.println("Cannot delete from an empty "
+ "list.");
else
if (first.info.equals(deleteItem)) //Case 2
first = first.link;
if (first == null) //the list had only one node
last = null;
count--;
else //search the list for the given info
found = false;
trailCurrent = first; //set trailCurrent to
//point to the first node
current = first.link; //set current to point to
//the second node
while (current != null && !found)
if (current.info.equals(deleteItem))
found = true;
else
trailCurrent = current;
current = current.link;
}//end while
if (found) //Case 3; if found, delete the node
count--;
trailCurrent.link = current.link;
if (last == current) //node to be deleted
//was the last node
last = trailCurrent; //update the value
//of last
else
System.out.println("Item to be deleted is "
+ "not in the list.");
}//end else
}//end else
}//end deleteNode
public void splitAt(LinkedListClass<T> secondList, T item)
LinkedListNode<T> current;
LinkedListNode<T> trailCurrent;
int i;
boolean found;
if (first==null)
System.out.println("Empty.");
first=null;
last=null;
count--;
else
current=first;
found=false;
i=1;
while(current !=null &&!found)
if(current.info.equals(secondList))
found= true;
else
trailCurrent=current;
i++;
if(found)
if(first==current)
first=first;
last=last;
count=count;
count=0;
else
first=current;
last=last;
last=null;
count = count- i+1;
count = i-1;
else
System.out.println("Item to be split at is "
+ "not in the list.");
first=null;
last=null;
count=0;
}I dont have a test program at all. The program is supposed to prompt for user input of numbers. (it does) Take the input and end at input of -999 (it does). Then it asks user where it wants to split list (it does). When I enter a number it does nothing after that. I am going to post updated code and see if that helps along with all the classes. Thanks!
This is the class to prompt:
import java.util.*;
public class Ch16_ProgEx6
static Scanner console = new Scanner(System.in);
public static void main(String[] args)
UnorderedLinkedList<Integer> list
= new UnorderedLinkedList<Integer>();
UnorderedLinkedList<Integer> subList =
new UnorderedLinkedList<Integer>();
Integer num;
System.out.println("Enter integers ending with -999.");
num = console.nextInt();
while (num != -999)
list.insertLast(num);
num = console.nextInt();
System.out.println();
System.out.println("list: ");
list.print();
System.out.println();
System.out.println("Length of list: " + list.length());
System.out.print("Enter the number at which to split list: ");
num = console.nextInt();
list.splitAt(subList, num);
System.out.println("Lists after splitting list");
System.out.print("list: ");
list.print();
System.out.println();
System.out.println("Length of list: " + list.length());
System.out.print("sublist: ");
subList.print();
System.out.println();
System.out.println("Length of sublist: " + subList.length());
}This is the ADT:
public interface LinkedListADT<T> extends Cloneable
public Object clone();
//Returns a copy of objects data in store.
//This method clones only the references stored in
//each node of the list. The objects that the
//list nodes point to are not cloned.
public boolean isEmptyList();
//Method to determine whether the list is empty.
//Postcondition: Returns true if the list is empty;
// false otherwise.
public void initializeList();
//Method to initialize the list to an empty state.
//Postcondition: The list is initialized to an empty
// state.
public void print();
//Method to output the data contained in each node.
public int length();
//Method to return the number of nodes in the list.
//Postcondition: The number of nodes in the list is
// returned.
public T front();
//Method to return a reference of the object containing
//the data of the first node of the list.
//Precondition: The list must exist and must not be empty.
//Postcondition: The reference of the object that
// contains the info of the first node
// is returned.
public T back();
//Method to return a reference of object containing
//the data of the last node of the list.
//Precondition: The list must exist and must not be empty.
//Postcondition: The reference of the object that
// contains the info of the last node
// is returned.
public boolean search(T searchItem);
//Method to determine whether searchItem is in the list.
//Postcondition: Returns true if searchItem is found
// in the list; false otherwise.
public void insertFirst(T newItem);
//Method to insert newItem in the list.
//Postcondition: newItem is inserted at the
// beginning of the list.
public void insertLast(T newItem);
//Method to insert newItem at the end of the list.
//Postcondition: newItem is inserted at the end
// of the list.
public void deleteNode(T deleteItem);
//Method to delete deleteItem from the list.
//Postcondition: If found, the node containing
// deleteItem is deleted from the
// list.
public void splitAt(LinkedListClass<T> secondList, T item);
}This is the linked list class:
import java.util.NoSuchElementException;
public abstract class LinkedListClass<T> implements LinkedListADT<T>
protected class LinkedListNode<T> implements Cloneable
public T info;
public LinkedListNode<T> link;
//Default constructor
//Postcondition: info = null; link = null;
public LinkedListNode()
info = null;
link = null;
//Constructor with parameters
//This method sets info pointing to the object to
//which elem points to and link is set to point to
//the object to which ptr points to.
//Postcondition: info = elem; link = ptr;
public LinkedListNode(T elem, LinkedListNode<T> ptr)
info = elem;
link = ptr;
//Returns a copy of objects data in store.
//This method clones only the references stored in
//the node. The objects that the nodes point to
//are not cloned.
public Object clone()
LinkedListNode<T> copy = null;
try
copy = (LinkedListNode<T>) super.clone();
catch (CloneNotSupportedException e)
return null;
return copy;
//Method to return the info as a string.
//Postcondition: info as a String object is
// returned.
public String toString()
return info.toString();
} //end class LinkedListNode
public class LinkedListIterator<T>
protected LinkedListNode<T> current; //variable to
//point to the
//current node in
//list
protected LinkedListNode<T> previous; //variable to
//point to the
//node before the
//current node
//Default constructor
//Sets current to point to the first node in the
//list and sets previous to null.
//Postcondition: current = first; previous = null;
public LinkedListIterator()
current = (LinkedListNode<T>) first;
previous = null;
//Method to reset the iterator to the first node
//in the list.
//Postcondition: current = first; previous = null;
public void reset()
current = (LinkedListNode<T>) first;
previous = null;
//Method to return a reference of the info of the
//current node in the list and to advance iterator
//to the next node.
//Postcondition: previous = current;
// current = current.link;
// A refrence of the current node
// is returned.
public T next()
if (!hasNext())
throw new NoSuchElementException();
LinkedListNode<T> temp = current;
previous = current;
current = current.link;
return temp.info;
//Method to determine whether there is a next
//element in the list.
//Postcondition: Returns true if there is a next
// node in the list; otherwise
// returns false.
public boolean hasNext()
return (current != null);
//Method to remove the node currently pointed to
//by the iterator.
//Postcondition: If iterator is not null, then the
// node that the iterator points to
// is removed. Otherwise the method
// throws NoSuchElementException.
public void remove()
if (current == null)
throw new NoSuchElementException();
if (current == first)
first = first.link;
current = (LinkedListNode<T>) first;
previous = null;
if (first == null)
last = null;
else
previous.link = current.link;
if (current == last)
last = first;
while (last.link != null)
last = last.link;
current = current.link;
count--;
//Method to return the info as a string.
//Postcondition: info as a String object is returned.
public String toString()
return current.info.toString();
} //end class LinkedListIterator
//Instance variables of the class LinkedListClass
protected LinkedListNode<T> first; //variable to store the
//address of the first
//node of the list
protected LinkedListNode<T> last; //variable to store the
//address of the last
//node of the list
protected int count; //variable to store the number of
//nodes in the list
//Default constructor
//Initializes the list to an empty state.
//Postcondition: first = null, last = null,
// count = 0
public LinkedListClass()
first = null;
last = null;
count = 0;
//Method to determine whether the list is empty.
//Postcondition: Returns true if the list is empty;
// false otherwise.
public boolean isEmptyList()
return (first == null);
//Method to initialize the list to an empty state.
//Postcondition: first = null, last = null,
// count = 0
public void initializeList()
first = null;
last = null;
count = 0;
//Method to output the data contained in each node.
public void print()
LinkedListNode<T> current; //variable to traverse
//the list
current = first; //set current so that it points to
//the first node
while (current != null) //while more data to print
System.out.print(current.info + " ");
current = current.link;
}//end print
//Method to return the number of nodes in the list.
//Postcondition: The value of count is returned.
public int length()
return count;
//Method to return a reference of the object containing
//the data of the first node of the list.
//Precondition: The list must exist and must not be empty.
//Postcondition: The reference of the object that
// contains the info of the first node
// is returned.
public T front()
return first.info;
//Method to return a reference of object containing
//the data of the last node of the list.
//Precondition: The list must exist and must not be empty.
//Postcondition: The reference of the object that
// contains the info of the last node
// is returned.
public T back()
return last.info;
//Returns a copy of objects data in store.
//This method clones only the references stored in
//each node of the list. The objects that the
//list nodes point to are not cloned.
public Object clone()
LinkedListClass<T> copy = null;
try
copy = (LinkedListClass<T>) super.clone();
catch (CloneNotSupportedException e)
return null;
//If the list is not empty clone each node of
//the list.
if (first != null)
//Clone the first node
copy.first = (LinkedListNode<T>) first.clone();
copy.last = copy.first;
LinkedListNode<T> current;
if (first != null)
current = first.link;
else
current = null;
//Clone the remaining nodes of the list
while (current != null)
copy.last.link =
(LinkedListNode<T>) current.clone();
copy.last = copy.last.link;
current = current.link;
return copy;
//Method to return an iterator of the list.
//Postcondition: An iterator is instantiated and
// returned.
public LinkedListIterator<T> iterator()
return new LinkedListIterator<T>();
//Method to determine whether searchItem is in
//the list.
//Postcondition: Returns true if searchItem is found
// in the list; false otherwise.
public abstract boolean search(T searchItem);
//Method to insert newItem in the list.
//Postcondition: first points to the new list
// and newItem is inserted at the
// beginning of the list. Also,
// last points to the last node and
// count is incremented by 1.
public abstract void insertFirst(T newItem);
//Method to insert newItem at the end of the list.
//Postcondition: first points to the new list and
// newItem is inserted at the end
// of the list. Also, last points to
// the last node and
// count is incremented by 1.
public abstract void insertLast(T newItem);
//Method to delete deleteItem from the list.
//Postcondition: If found, the node containing
// deleteItem is deleted from the
// list. Also, first points to the first
// node, last points to the last
// node of the updated list, and count
// is decremented by 1.
public abstract void deleteNode(T deleteItem);
public abstract void splitAt(LinkedListClass<T> secondList, T item);
}And this is the UnorderedLinked Class with the very last method the one being Im stuck on. The SplitAt Method.
public class UnorderedLinkedList<T> extends LinkedListClass<T>
//Default constructor
public UnorderedLinkedList()
super();
//Method to determine whether searchItem is in
//the list.
//Postcondition: Returns true if searchItem is found
// in the list; false otherwise.
public boolean search(T searchItem)
LinkedListNode<T> current; //variable to traverse
//the list
boolean found;
current = first; //set current to point to the first
//node in the list
found = false; //set found to false
while (current != null && !found) //search the list
if (current.info.equals(searchItem)) //item is found
found = true;
else
current = current.link; //make current point to
//the next node
return found;
//Method to insert newItem in the list.
//Postcondition: first points to the new list
// and newItem is inserted at the
// beginning of the list. Also,
// last points to the last node and
// count is incremented by 1.
public void insertFirst(T newItem)
LinkedListNode<T> newNode; //variable to create the
//new node
newNode =
new LinkedListNode<T>(newItem, first); //create and
//insert newNode before
//first
first = newNode; //make first point to the
//actual first node
if (last == null) //if the list was empty, newNode is
//also the last node in the list
last = newNode;
count++; //increment count
//Method to insert newItem at the end of the list.
//Postcondition: first points to the new list and
// newItem is inserted at the end
// of the list. Also, last points to
// the last node and
// count is incremented by 1.
public void insertLast(T newItem)
LinkedListNode newNode; //variable to create the
//new node
newNode =
new LinkedListNode(newItem, null); //create newNode
if (first == null) //if the list is empty, newNode is
//both the first and last node
first = newNode;
last = newNode;
else //if the list is not empty, insert
//newNode after last
last.link = newNode; //insert newNode after last
last = newNode; //set last to point to the
//actual last node
count++;
}//end insertLast
//Method to delete deleteItem from the list.
//Postcondition: If found, the node containing
// deleteItem is deleted from the
// list. Also, first points to the first
// node, last points to the last
// node of the updated list, and count
// is decremented by 1.
public void deleteNode(T deleteItem)
LinkedListNode<T> current; //variable to traverse
//the list
LinkedListNode<T> trailCurrent; //variable just
//before current
boolean found;
if ( first == null) //Case 1; the list is empty
System.err.println("Cannot delete from an empty "
+ "list.");
else
if (first.info.equals(deleteItem)) //Case 2
first = first.link;
if (first == null) //the list had only one node
last = null;
count--;
else //search the list for the given info
found = false;
trailCurrent = first; //set trailCurrent to
//point to the first node
current = first.link; //set current to point to
//the second node
while (current != null && !found)
if (current.info.equals(deleteItem))
found = true;
else
trailCurrent = current;
current = current.link;
}//end while
if (found) //Case 3; if found, delete the node
count--;
trailCurrent.link = current.link;
if (last == current) //node to be deleted
//was the last node
last = trailCurrent; //update the value
//of last
else
System.out.println("Item to be deleted is "
+ "not in the list.");
}//end else
}//end else
}//end deleteNode
public void splitAt(LinkedListClass<T> secondList, T item)
LinkedListNode<T> current;
LinkedListNode<T> trailCurrent;
int i;
boolean found;
if (first==null)
System.out.println("Empty.");
first=null;
last=null;
count--;
count=0;
else
current=first;
found=false;
i=1;
while(current !=null &&!found)
if(current.info.equals(item))
found= true;
else
trailCurrent=first;
current=first;
i++;
if(found)
if(first==current)
first.link=first;
last.link=last;
count--;
count=0;
else
first.link=current;
last.link=last;
last=null;
count = count- i+1;
count = i-1;
} else {
System.out.println("Item to be split at is "
+ "not in the list.");
first=null;
last=null;
count=0;
Any help or just advice would be fine. Im not the best at Java, better at VB. Am completely stumped! Thanks so much! -
Recursively Finding a Node in a Linked List
I'm trying to find a node recursively in this linked list but keep coming up with an error message - can anyone tell me what is wrong?
public boolean find (Object obj)
DonorNode node = new DonorNode(obj);
DonorNode current = list;
if (don.equals(current))
return true;
else
return find(current.next);
}Please post within code tags (button above the message box).
Without more information it's hard to say.
What is list?
What is don?
If you don't mind me pointing out:
A method named find conventionally returns some object it is searching for or null if not found.
What you have (by that I mean a method returning boolean) is generally named contains (or some other obvious predicate name).
That being said, if I assume that DonorNodes contain some Object and have getter functions to access those; and that list is a DonorNode representing the head of the list, try something like:public boolean contains(Object o) {
return contains(o, list);
private boolean contains(Object o, DonorNode n) {
if (n.getObject() == o)
return true;
if (n.getNext() == null)
return false;
return contains(o, n.getNext());
}Although keep in mind that comparing two Objects using '==' will result in reference only comparison. If you need some other form of comparison you might consider using the equals method (make sure you then implement it in all potentially contained classes) or even narrowing the accepted argument to classes that implement the Comparable interface.
Hope this helps. -
Linked List - deleeting nodes - HELP!
How do I delete all occurences of the nodes with the same parameters in the linked list ?
example:
Node1-> Node2 ->Node3->Node4->Node5
Node1, Node4, and Node5 have the same String value, how do I delete them in one method without breaking the linked list ?
thanksHi,
You have iterate thru the linked list remove one by one. Also have look at other collection classes like HashSet or HashMap for fast retrieval. -
Hello,
I have a double linked list where I want to change one node to another and change its references at the same time.
The nodes are not together i.e. they do not appear in the list consectutively.
I need to swap like B and D - I have managed to do swaps like A and B, and C and D (that took a while).
Is this logic correct (I am using temporary nodes):
if(f1 != (f2 - 1))
Object temp = object1;
Object temp2 = object2;
object1.getPrevious().setNext(object2);
object2.getNext().setPrevious(object1);
object1.getNext().setPrevious(object2);
object2.getPrevious().setNext(object1);
object1.setPrevious(temp2.getPrevious());
object1.setNext(temp2.getNext());
object2.setPrevious(temp.getPrevious());
object2.setNext(temp.getNext());
If this logic is not correct then please only give hints as to why.
CheersHello,
I have a double linked list where I want to change
one node to another and change its references at the
same time.
The nodes are not together i.e. they do not appear in
the list consectutively.
I need to swap like B and D - I have managed to do
swaps like A and B, and C and D (that took a while).
Is this logic correct (I am using temporary nodes):
if(f1 != (f2 - 1))
Object temp = object1;
Object temp2 = object2;
object1.getPrevious().setNext(object2);
object2.getNext().setPrevious(object1);
object1.getNext().setPrevious(object2);
object2.getPrevious().setNext(object1);
object1.setPrevious(temp2.getPrevious());
object1.setNext(temp2.getNext());
object2.setPrevious(temp.getPrevious());
object2.setNext(temp.getNext());
If this logic is not correct then please only give
hints as to why.
CheersI didn't check your logic, but I think that there are errors in it since I saw these lines:
object1.setPrevious(temp2.getPrevious());
object1.setNext(temp2.getNext());
object2.setPrevious(temp.getPrevious());
object2.setNext(temp.getNext()); temp and temp2 are not copies of object1 and object2. They are references to the same object, so when you do e.g. object1.getPrevious().setNext() you also change previous->next for temp.
temp == object1
temp2 == object2
Kaj -
Why am I doing this - in reference to Linked List Assignment
So I have a programming assignment to do for class, and in it the instructor wants us to write our own class for LinkedList. Upon browsing the java library I found that there is a java.util.LinkedList class with appropriate methods already defined. Is my instructor crazy or just outdated, I can see the point in writing one, to better understand the Linked List, but the one in the library is probably better anyway.
Is there a way to peek inside the code for java.util.LinkedList to at least get an idea of how I should start writing this class?
Thank You.baftos wrote:
datawerd wrote:
So I have a programming assignment to do for class, and in it the instructor wants us to write our own class for LinkedList. Upon browsing the java library I found that there is a java.util.LinkedList class with appropriate methods already defined. Is my instructor crazy or just outdated, I can see the point in writing one, to better understand the Linked List, but the one in the library is probably better anyway.
Is there a way to peek inside the code for java.util.LinkedList to at least get an idea of how I should start writing this class?Yes, there is a way and, unlike others, I admire your approach. It's so refreshing after seeing all the 'do my homework' krapp. I call this reasearch, not cheating. Go to your JDK directory and open src.zip.
You will find there what you need. And by the way, peeking inside this zip would answer hundreds of questions,
Whenever I don't quite know how to do something, I try to find a similar API class and just see how Sun does it.
Edited by: baftos on Oct 16, 2007 10:46 PMYeah man, I'm with you on this one. I don't consider it cheating at all (given that you could find it on Wikipedia anyway), and I learn by example.
Apache taught me how to make an LRU cache the other day. Thanks Apache!
EDIT: To the OP: by the way, the LRU algorithm uses a modified linked list that I wouldn't have understood if i hadn't done my work in grade 12 / first year com-sci courses.
Edited by: endasil on Oct 16, 2007 8:12 PM -
Replace node in a linked list.
Hello everyone,
Im trying to replace a node with the following method :
@Override
public boolean replace(Object oneThing) {
Node aNode = find(oneThing); // gets a node previous to oneThing
if(aNode == null)
return false;
oneThing = aNode.next.next;
aNode.next = (Node) ((Copyable) oneThing).copy();
return true;
}I keep getting this error and dont know how to fix it or what im doing wrong:
Exception in thread "main" java.lang.ClassCastException: myContainers.List$Node cannot be cast to myUtils.CopyableAny help is greatly appreciated.Nevermind I got It! thanks
-
How to print the contents of doubly-Linked List
Hi
I have a DLList consists of header , trailer and 10 linked nodes in between
Is there a simple way to print the contents ie "the elements"
of the list
thanksIn general you should write an iterator for every linked data structure for fast traversal. I'm guessing you're writing your own DLL for an assignment because one normally uses the LinkedList structure that is included in the api. Anyway, here is an example of how the iterator is implemented for a double linked list:
http://www.theparticle.com/_javadata2.html#Doubly_Linked_Lists_with_Enumeration -
Help needed in linked lists...
I have been working on this computer assignment lately but I still don't understand linked lists yet..I did an assignment on array based implementation and now I am supposed to do the same thing in linked list implementation..
I need help on how to change this into a linked list implementation..any help would be appreciated. Thank you..below is the code for the array based implementation..the only thing that needs change here is after where is says Array-based implementation of the ADT list.
public class ListArrayBasedDriver {
public static void main(String [] args) {
ListArrayBased myGroceryList = new ListArrayBased();
myGroceryList.add(1,"milk");
myGroceryList.add(2,"eggs");
myGroceryList.add(3,"butter");
myGroceryList.add(4,"pecans");
myGroceryList.add(5,"apples");
myGroceryList.add(6,"bread");
myGroceryList.add(7,"chicken");
myGroceryList.add(8,"rice");
myGroceryList.add(9,"red beans");
myGroceryList.add(10,"sausage");
myGroceryList.add(11,"flour");
printList(myGroceryList); //print out original List
System.out.print("numItems is now: " + myGroceryList.size() + "\n");
System.out.println("adding juice for 5th item...");
myGroceryList.add (5, (Object) "juice"); //add juice
System.out.println("item 5 is: " + myGroceryList.get(5)); //get position 5
printList(myGroceryList);
System.out.print("numItems is now: " + myGroceryList.size() + "\n");
System.out.println("removing juice...");
myGroceryList.remove (5); //remove item at position 5
printList(myGroceryList);
System.out.print("numItems is now: " + myGroceryList.size() + "\n");
public static void printList(ListArrayBased myList)
//method prints a list, numbering the values, e.g, "1. milk" .... "5. juice".... etc.
int i;
for(i=1; i <= myList.size(); i++)
String tempString = new String((String)myList.get(i));
System.out.println(i+" "+ tempString);
// Array-based implementation of the ADT list.
class ListArrayBased {
private static final int MAX_LIST = 50;
private Object items[]; // an array of list items
private int numItems; // number of items in list
public ListArrayBased()
// creates an empty list
items = new Object[MAX_LIST];
numItems = 0;
} // end default constructor
public boolean isEmpty()
return (numItems == 0);
} // end isEmpty
public int size()
return numItems;
} // end size
public void removeAll()
// Creates a new array; marks old array for
// garbage collection.
items = new Object[MAX_LIST];
numItems = 0;
} // end removeAll
public void add(int index, Object item) throws ListIndexOutOfBoundsException
if (numItems > MAX_LIST)
throw new ListException("ListException on add");
} // end if
if (index >= 1 && index <= numItems+1)
// make room for new element by shifting all items at
// positions >= index toward the end of the
// list (no shift if index == numItems+1)
for (int pos = numItems; pos >= index; pos--) {
items[translate(pos+1)] = items[translate(pos)];
} // end for
// insert new item
items[translate(index)] = item;
numItems++;
else
{ // index out of range
throw new ListIndexOutOfBoundsException(
"ListIndexOutOfBoundsException on add");
} // end if
} //end add
public Object get(int index) throws ListIndexOutOfBoundsException
if (index >= 1 && index <= numItems)
return items[translate(index)];
else
{ // index out of range
throw new ListIndexOutOfBoundsException(
"ListIndexOutOfBoundsException on get");
} // end if
} // end get
public void remove(int index) throws ListIndexOutOfBoundsException
if (index >= 1 && index <= numItems)
// delete item by shifting all items at
// positions > index toward the beginning of the list
// (no shift if index == size)
for (int pos = index+1; pos <= size(); pos++) {
items[translate(pos-1)] = items[translate(pos)];
} // end for
numItems--;
else
{ // index out of range
throw new ListIndexOutOfBoundsException("ListIndexOutOfBoundsException on remove");
} // end if
} // end remove
private int translate(int position) {
return position - 1;
} // end translate
} // end ListArrayBased
class ListException extends RuntimeException
public ListException(String s)
super(s);
} // end constructor
} // end ListException
class ListIndexOutOfBoundsException
extends IndexOutOfBoundsException {
public ListIndexOutOfBoundsException(String s) {
super(s);
} // end constructor
} // end ListIndexOutOfBoundsExceptionCould someone check for me if this will work and if it doesn't what I need to do to make it work..Thanks...
public class ListArrayBasedDriver {
public static void main(String [] args) {
ListArrayBased myGroceryList = new ListArrayBased();
myGroceryList.add(1,"milk");
myGroceryList.add(2,"eggs");
myGroceryList.add(3,"butter");
myGroceryList.add(4,"pecans");
myGroceryList.add(5,"apples");
myGroceryList.add(6,"bread");
myGroceryList.add(7,"chicken");
myGroceryList.add(8,"rice");
myGroceryList.add(9,"red beans");
myGroceryList.add(10,"sausage");
myGroceryList.add(11,"flour");
printList(myGroceryList); //print out original List
System.out.print("numItems is now: " + myGroceryList.size() + "\n");
System.out.println("adding juice for 5th item...");
myGroceryList.add (5, (Object) "juice"); //add juice
System.out.println("item 5 is: " + myGroceryList.get(5)); //get position 5
printList(myGroceryList);
System.out.print("numItems is now: " + myGroceryList.size() + "\n");
System.out.println("removing juice...");
myGroceryList.remove (5); //remove item at position 5
printList(myGroceryList);
System.out.print("numItems is now: " + myGroceryList.size() + "\n");
public static void printList(ListArrayBased myList)
//method prints a list, numbering the values, e.g, "1. milk" .... "5. juice".... etc.
int i;
for(i=1; i <= myList.size(); i++)
String tempString = new String((String)myList.get(i));
System.out.println(i+" "+ tempString);
// Linked List-based implementation of the ADT list.
class ListNode
//class to represent one node in a list
class ListNode
//package access members; List can access these directly
Object data;
ListNode nextNode;
//contructor creates a ListNode that refers to object
ListNode( Object object)
this( object, null );
} //end ListNode one-argument constructor
//constructor creates ListNode that refers to
// Object and to the next ListNode
ListNode ( Object object, ListNode node)
data = object;
nextNode = node;
// end ListNode two-argument contructor
//return reference to data in node
Object getObject()
return data; // return Object in this mode
//return reference to next node in list
ListNode getNext()
return nextNode; // get next node
} // end method getNext
} //end class ListNode
//class List Definition
public class List
private ListNode firstNode;
private ListNode lastNode;
private String name; // string like " list " used in printing
//contructor creates empty List with " list " as the name
public List()
this(" list ");
} //end List no-arguement constructor
//contructor creates an empty list with a name
public List( String listName )
name = listname;
firstNode = lastNode = null;
} //end List no-arguement contructor
//insert Object at front of List
public void insertAtFront ( object insertItem )
if ( isEmpty() ) //firstNode and lastNode refer to same object
firstNode = lastNode = newListNode( insertItem );
else // firstNode refers to new node
firstNode = new ListNode ( insertItem, firstNode );
} // end method insertAtFront
// insert Object at end of List
public void insert AtBack ( Object insertItem )
if ( isEmpty() ) //firstNode and lastNode refer to same object
firstNode = new ListNode ( insertItem );
else // firstNode refers to new node
firstNode = new ListNode (insertItem, firstNode );
} // end method insertAtFront
// insert Object at end of List
public void insertAtBack ( Object insertItem )
if ( isEmpty() ) //firstNode and LastNode refer to same Object
firstNode = lastNode = new ListNode ( insertItem );
else // lastNode = lastNode.nextNode = new ListNode ( insertItem );
} // end method insertAtBack
//remove first node from List
public Object removeFromFront() throws EmptyListException
if( isEmpty() ) //throw exception if list is empty
throw new EmptyListException( name );
object removedItem = firstNode.data; //retrieve data being removed
// update references firstNode and lastNode
if (firstNode == lastNode )
firstNode =lastNode = null;
else
firstNode = firstNode.nextNode;
return removedItem; // return removed node data
} //end method removeFromFront
//remove last node from List
Public Object removeFromBack() throws EmptyListException
If ( isEmpty() ) // throw exception if list is empty
throw new EmptyListException( name );
Object removedItem = lastNode.data; // retrieve data being removed
// update references firstNode and lastNode
If ( firstNode == lastNode )
firstNode = lastNode = null;
else // locate new last node
ListNode current = firstNode;
// loop while current node does not refer to lastNode
while ( current.nextNode != lastNode )
current = current.nextNode;
lastNode = current; // current is new lastNode
current.nextNode = null;
} // end else
return removedItem; // return removed node data
} // end method removeFromBack
// determine whether list is empty
public boolean isEmpty()
return firstNode == null; // return true if list is empty
} // end method isEmpty
//output List contents
public void print()
if (isEmpty() )
System.out.printf(�Empty %s\n�, name );
return;
System.out.printf(�The %s is: �, name );
ListNode current = firstNode;
//while (current != null )
System.out,printf(�%s �, current.data );
current = current.nextNode;
} //end while
System.out.println( �\n� );
} //end method print
} end class List -
Alphabetizing a linked list, HELP!
To all:
Firstly, I'm not looking for someone to do my assignment for me. I just need a push in the right direction...
I need to create a linked list that contains nodes of a single string (a first name), but that list needs to be alphabetized and that's where I am stuck.
I can use an iterator method that will display a plain-old "make a new node the head" linked list with no problem. But I'm under the impression that an iterator method is also the way to go in alphabetizing this list (that is using an iterative method to determine the correct place to place a new node in the linked list). And I am having zero luck doing that.
The iterator method looks something like this:
// ---- MyList: DisplayList method ----
void DisplayList()
ListNode p;
for (ResetIterator(); (p = Iterate()) != null; )
p.DisplayNode();
// ---- MyList: ResetIterator method ----
void ResetIterator()
current = head;
// ---- MyList: Iterate method ----
ListNode Iterate()
if (current != null)
current = current.next;
return current;
Can I use the same iterator method to both display the final linked list AND alphabetize my linked list or do I need to create a whole new iterator method, one for each?
Please, someone give me a hint where to go with this. I've spent something like 15 hours so far trying to figure this thing out and I'm just stuck.
Thanks so much,
John
[email protected]I'll try and point you in the right direction without being too explicit as you request.
Is your "linked list" an instance of the Java class java.util.LinkedList or a class of your own?
If it is the Java class, then check out some of the other types of Collections that provide built-in sorting. You should be able to easily convert from your List to another type of Collection and back again to implement the sorting. (hint: you can do this in two lines of code).
If this is your own class and you want to code the sort yourself, implement something simple such as a bubble sort (should be easy to research on the web).
Converting to an array, sorting that and converting back is another option.
Good Luck. -
Linked lists problem -- help needed
Hello again. I've got yet another problem in my C++ course that stems from my use of a Mac instead of Windows. I'm going to install Parallels so I can get Windows on my MacBook and install Visual Studio this week so that I don't have to deal with these discrepancies anymore, but in the meanwhile, I'm having a problem here that I don't know how to resolve. To be clear, I've spent a lot of time trying to work this out myself, so I'm not just throwing this up here to have you guys do the work for me -- I'm really stuck here, and am coming here as a last resort, so I'll be very, very appreciative for any help that anyone can offer.
In my C++ course, we are on a chapter about linked lists, and the professor has given us a template to make the linked lists work. It comes in three files (a header, a source file, and a main source file). I've made some adjustments -- the original files the professor provided brought up 36 errors and a handful of warnings, but I altered the #include directives and got it down to 2 errors. The problematic part of the code (the part that contains the two errors) is in one of the function definitions, print_list(), in the source file. That function definition is shown below, and I've marked the two statements that have the errors using comments that say exactly what the errors say in my Xcode window under those two statements. If you want to see the entire template, I've pasted the full code from all three files at the bottom of this post, but for now, here is the function definition (in the source file) that contains the part of the code with the errors:
void LinkedList::printlist( )
// good for only a few nodes in a list
if(isEmpty() == 1)
cout << "No nodes to display" << endl;
return;
for(CURSOR = FRONT_ptr; CURSOR; CURSOR = CURSOR-> link)
{ cout << setw(8) << CURSOR->name; } cout << endl; // error: 'setw' was not declared in this scope
for(CURSOR = FRONT_ptr; CURSOR; CURSOR = CURSOR-> link)
{ cout << setw(8) << CURSOR->test_grade; } cout << endl; // error: 'setw' was not declared in this scope
As you can see, the problem is with the two statements that contain the 'setw' function. Can anyone help me figure out how to get this template working and get by these two errors? I don't know enough about linked lists to know what I can and can't mess with here to get it working. The professor recommended that I try using 'printf' instead of 'cout' for those two statements, but I don't know how to achieve the same effect (how to do whatever 'setw' does) using 'printf'. Can anyone please help me get this template working? Thank you very, very much.
For reference, here is the full code from all three files that make up the template:
linkedlist.h (header file):
#ifndef LINKED_LINKED_H
#define LINKED_LINKED_H
struct NODE
string name;
int test_grade;
NODE * link;
class Linked_List
public:
Linked_List();
void insert(string n, int score);
void remove(string target);
void print_list();
private:
bool isEmpty();
NODE *FRONT_ptr, *REAR_ptr, *CURSOR, *INSERT, *PREVIOUS_ptr;
#endif
linkedlist.cpp (source file):
#include <iostream>
using namespace std;
#include "linkedlist.h"
LinkedList::LinkedList()
FRONT_ptr = NULL;
REAR_ptr = NULL;
PREVIOUS_ptr = NULL;
CURSOR = NULL;
void Linked_List::insert(string n, int score)
INSERT = new NODE;
if(isEmpty()) // first item in List
// collect information into INSERT NODE
INSERT-> name = n;
// must use strcpy to assign strings
INSERT -> test_grade = score;
INSERT -> link = NULL;
FRONT_ptr = INSERT;
REAR_ptr = INSERT;
else // else what?? When would this happen??
// collect information into INSERT NODE
INSERT-> name = n; // must use strcpy to assign strings
INSERT -> test_grade = score;
REAR_ptr -> link = INSERT;
INSERT -> link = NULL;
REAR_ptr = INSERT;
void LinkedList::printlist( )
// good for only a few nodes in a list
if(isEmpty() == 1)
cout << "No nodes to display" << endl;
return;
for(CURSOR = FRONT_ptr; CURSOR; CURSOR = CURSOR-> link)
{ cout << setw(8) << CURSOR->name; } cout << endl; // error: 'setw' was not declared in this scope
for(CURSOR = FRONT_ptr; CURSOR; CURSOR = CURSOR-> link)
{ cout << setw(8) << CURSOR->test_grade; } cout << endl; // error: 'setw' was not declared in this scope
void Linked_List::remove(string target)
// 3 possible places that NODES can be removed from in the Linked List
// FRONT
// MIDDLE
// REAR
// all 3 condition need to be covered and coded
// use Trasversing to find TARGET
PREVIOUS_ptr = NULL;
for(CURSOR = FRONT_ptr; CURSOR; CURSOR = CURSOR-> link)
if(CURSOR->name == target) // match
{ break; } // function will still continue, CURSOR will
// mark NODE to be removed
else
{ PREVIOUS_ptr = CURSOR; } // PREVIOUS marks what NODE CURSOR is marking
// JUST before CURSOR is about to move to the next NODE
if(CURSOR == NULL) // never found a match
{ return; }
else
// check each condition FRONT, REAR and MIDDLE
if(CURSOR == FRONT_ptr)
// TARGET node was the first in the list
FRONT_ptr = FRONT_ptr -> link; // moves FRONT_ptr up one node
delete CURSOR; // deletes and return NODE back to free memory!!!
return;
}// why no need for PREVIOUS??
else if (CURSOR == REAR_ptr) // TARGET node was the last in the list
{ // will need PREVIOUS for this one
PREVIOUS_ptr -> link = NULL; // since this node will become the last in the list
REAR_ptr = PREVIOUS_ptr; // = REAR_ptr; // moves REAR_ptr into correct position in list
delete CURSOR; // deletes and return NODE back to free memory!!!
return;
else // TARGET node was the middle of the list
{ // will need PREVIOUS also for this one
PREVIOUS_ptr -> link = CURSOR-> link; // moves PREV nodes' link to point where CURSOR nodes' points
delete CURSOR; // deletes and return NODE back to free memory!!!
return;
bool Linked_List::isEmpty()
if ((FRONT_ptr == NULL) && (REAR_ptr == NULL))
{ return true; }
else
{ return false;}
llmain.cpp (main source file):
#include <iostream>
#include <string>
#include <iomanip>
using namespace std;
#include "linkedlist.h"
int main()
Linked_List one;
one.insert("Angela", 261);
one.insert("Jack", 20);
one.insert("Peter", 120);
one.insert("Chris", 270);
one.print_list();
one.remove("Jack");
one.print_list();
one.remove("Angela");
one.print_list();
one.remove("Chris");
one.print_list();
return 0;setw is the equivalent of the field width value in printf. In your code, the printf version would look like:
printf("%8s", CURSOR->name.c_str());
I much prefer printf over any I/O formatting in C++. See the printf man page for more information. I recommend using Bwana: http://www.bruji.com/bwana/
I do think it is a good idea to verify your code on the platform it will be tested against. That means Visual Studio. However, you don't want to use Visual Studio. As you have found out, it gets people into too many bad habits. Linux is much the same way. Both development platforms are designed to build anything, whether or not it is syntactically correct. Both GNU and Microsoft have a long history of changing the language standards just to suit themselves.
I don't know what level you are in the class, but I have a few tips for you. I'll phrase them so that they answers are a good exercise for the student
* Look into const-correctness.
* You don't need to compare a bool to 1. You can just use bool. Plus, any integer or pointer type has an implicit cast to bool.
* Don't reuse your CURSOR pointer as a temporary index. Create a new pointer inside the for loop.
* In C++, a struct is the same thing as a class, with all of its members public by default. You can create constructors and member functions in a struct.
* Optimize your function arguments. Pass by const reference instead of by copy. You will need to use pass by copy at a later date, but don't worry about that now.
* Look into initializer lists.
* In C++ NULL and 0 are always the same.
* Return the result of an expression instead of true or false. Technically this isn't officially Return Value Optimization, but it is a good habit.
Of course, get it running first, then make it fancy. -
Alright, here's the problem. I have my linked list, either imported from a text file or inputted by the user. Now, I need to sort it by the date and the time strings... Yet, every time I do I get an NullPointException. Can anyone help? Here's my code for the list:
public class ListReferenceBased implements ListInterface{
//references to the linked list items
private Node head;
private int numItems; //number of items that exist in list
//Default Constructor
//sets both items to null
public ListReferenceBased(){
numItems = 0;
head = null;
//if the numItems in the list is empty
//returns true.
public boolean isEmpty(){
return numItems == 0;
// returns numItems, aka the size of the list
public int size(){
return numItems;
//finds a node by setting a node to the 'head'
// and loops through to the index 'resetting'
// curr to the 'next' node.
private Node find(int index){
Node curr = head;
for( int skip = 1; skip < index; skip++){
curr = curr.getNext();
return curr;
public Object get(int index)
throws ListIndexOutOfBoundsException{
//catches if list does not reach the index given
//loops through the index
if(index >= 1 && index <= numItems){
//sets curr to the index through find()
Node curr = find(index);
//sets dataitem to the current node
Object dataItem = curr.getItem();
return dataItem;
}else{
throw new ListIndexOutOfBoundsException("The List index is out of bounds on get");
public void add(int index, Object item)
throws ListIndexOutOfBoundsException{
//checks to make sure there are no nodes yet
//if there are inserts them in the list
//by moving
if(index >=1&& index<= numItems+1){
if(index==1){
// if no list exists
//creates a new node and sets it to head
Node newNode = new Node(item, head);
head = newNode;
}else{
//inserts the node at the index
//by finding it first
Node prev = find(index-1);
//creates a new node by placing the Object item
//and the 'new prev' node into a node
//'deleting' the old 'bonds'
Node newNode = new Node(item, prev.getNext());
rev.setNext(newNode);
//increments number of items in list
numItems++;
}else{
throw new ListIndexOutOfBoundsException("List index out of bounds");
public void remove(int index)
throws ListIndexOutOfBoundsException{
//catches the list if it doesn't exist
//checks to make sure list exists
if(index>=1&& index<= numItems){
//if only the head exists
//calls next node else moves
//the node away and moves the prev
//on up.
if(index==1){
head = head.getNext();
}else{
Node prev = find(index-1);
Node curr = prev.getNext();
prev.setNext(curr.getNext());
//decreases the number of items in list
numItems--;
}else{
throw new ListIndexOutOfBoundsException("List index out of bounds");
//sets the numItem to null telling the list it
//does not exist
public void removeAll(){
head = null;
numItems=0;
Yeah, unfortunately, I had to design my own linked list for my assignment (that's taken almost 40+ hours). So, now every alogrithm I've tried to write seems to give me a null pointer, for example this one
public void sort(){
//loop through all existing nodes
for(Node curr = head; curr != null; curr = curr.getNext()){
//parse the string of the current node
//to a string value
Node current = curr.getNext();
Node next = current.getNext();
Node temp;
String thisline = current.getItem().toString();
System.out.println(thisline);
StringTokenizer parser = new StringTokenizer ( thisline, "\t" );
String thisdate = parser.nextToken();
String thistime = parser.nextToken();
String thisline2 = next.getItem().toString();
System.out.println(thisline2);
StringTokenizer parser2 = new StringTokenizer ( thisline2, "\t" );
String thisdate2 = parser.nextToken();
String thistime2 = parser.nextToken();
//compares the dates of next in list
if(thisdate.compareTo(thisdate2)==1){
next.setNext(current);
current.setNext(next.getNext());
printList();
//if dates equal, compare the times
//if equal move to new position
//delete old position
}Pretty much I believe moving the positions is causing the problems after the first run around. Any suggestions?
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